heavy quark probes of hadronization of bulk matter at rhic
DESCRIPTION
Heavy Quark Probes of Hadronization of Bulk Matter at RHIC. Huan Zhong Huang Department of Physics and Astronomy University of California at Los Angeles Department of Engineering Physics Tsinghua University. Collisions at high p T (pQCD). - PowerPoint PPT PresentationTRANSCRIPT
Heavy Quark Probes of Hadronization of Bulk Matter
at RHIC
Huan Zhong Huang
Department of Physics and Astronomy
University of California at Los Angeles
Department of Engineering Physics
Tsinghua University
Collisions at high pCollisions at high pT T (pQCD)(pQCD)
)ˆˆˆ(),(
ˆˆˆ
),(),( 22
2/
2/3
3
utszDz
s
td
dxfxfdxdx
pd
dE hhc
h
cdab
bpbapaabcd
bah
h
At sufficiently large transverse momentum, let us consider the process:
p + p hadron + x
1) f(x,2) – parton structure function
2) ab->cd – pQCD calculable at large 2
3) D(zh,2) – Fragmentation function
To produce heavy quark pairs, the CM energy must>2m
Heavy Quark Production Mechanism
• Sensitive to initial gluon density and gluon distribution
0D
D0
J/
K+
l
l
K-
e-/-
e+/+
e-/-
e+/+
• Energy loss when propagating through dense medium
• Different scaling properties in central and forward region indicate shadowing, which can be due to CGC.
• Suppression or enhancement of charmonium in the medium is a critical signal for QGP.
• Sensitive to initial gluon density and gluon distribution
Parton Distribution Function Important
Uncertainties in gluon structure function of the proton
x
CTEQ5M1
CTEQ5HJ
MRST2001
Band – experimental constraints
J. Pumplin et al, JHEP07(2002)012
Fragmentation Functions
Fragmentation Functions from e+e Collisions
Belle Data
Charm Mesons from Hadronic Collisions
Charm meson pT ~ follow the NLO charm quark pT
-- add kT kick -- harder fragmentation ( func or recombination scheme)
kT Kick? What about kL?
The xF distribution matches the NLO charm quark xF !
Belle Puzzle !
PRL 89, 142001 (2002)
(e+e-J/ cc)(e+e-J/ X)
= 0.59 +0.15- 0.13 + 0.12-
An order of magnitude higher than theoretical predictions -- B.L. Ioffe and D.E. Kharzeev, PRD 69, 014016 (2004)
These results challenge our current understanding of how charm quarks/mesons are produced.
We may question our view for the underlying charm production process, e.g., the universality of fragmentation process and the fragmentation schemes !
K ~ 1.5
Neutral D mesons
LO QCD does not reproduce the cross sections !
K Factor !!
K ~ 4.5
Charged D mesons K factor energy, particle dependent !
Charm-Beauty different !
We don’t know the production mechanism at all !
Detecting D-Mesons via Hadronic Decays
• Hadronic Channels:– D0 K (B.R.: 3.8%) – D0 K (B.R.: 6.2% 100% () = 6.2%)– D K p (B.R.: 9.1%)– D*± D0π (B.R.: 68% 3.8% (D0 K ) = 2.6%) c p K (B.R.: 5%)
pc
xMxxP
0
0 exp)(
General Techniques for D Reconstruction
1. Identify charged daughter tracks through energy loss in TPC
2. Alternatively at high pT use h and assign referring mass (depends on analysis)
3. Produce invariant mass spectrum in same event
4. Obtain background spectrum via mixed event
5. Subtract background and get D spectrum
6. Often residual background to be eliminated by fit in region around the resonance
Exception D*: search for peak around m(D*)-m(D0) =0.1467 GeV/c2
D0
D0D*
Detecting Charm/Beauty via Semileptonic D/B Decays
• Semileptonic Channels:– D0 e+ + anything (B.R.: 6.87%) – D e + anything (B.R.: 17.2%)– B e + anything (B.R.: 10.2%)
single “non-photonic” electron continuum
• “Photonic” Single Electron Background: conversions (0 ) 0, Dalitz decays , , … decays (small)– Ke3 decays (small)
mBc
MmD
c
Mpc
xMxxP
/ MeV11)( ; / MeV15)(
exp)(
00
00
~7.6M AuAu 200GeV Run IV P05ia production 0~80% Min. Bias. |Vz| < 30cm
Electrons can be separated from pions. But the dEdx resolution is worse than d+Au
Log10(dEdx/dEdxBichsel) distribution is Gaussian.
2 Gauss can not describe the shoulder shape well. Exponential + Gaussian fit is used at lower pT region. 3 Gaussian fit is used at higher pT region.
2/ndf = 65/46
0.3<pT<4.0 GeV/c
TOF electron measurements
|1/-1|<0.03
2/ndf = 67/70
Mass(e+e-)<0.15 GeV/c2
Combinatorial background reconstructed by track rotating technique.
Invariant mass < 0.15 for photonic background.
γ conversion π0 Dalitz decay η Dalitz decay Kaon decay vector meson decays
Dominant source at low pT
Electron Spectrum
Charm pT Spectra
Power-law function with parameters dN/dy, <pT> and n to describe the D0 spectrum
D0 and e combined fit
Generate D0e decay kinematics according to the above parameters
Vary (dN/dy, <pT>, n) to get the min. 2 by comparing power-law to D0 data and the decayed e shape to e data
<pT>=1.20 0.05(stat.) GeV/c in minbias Au+Au
<pT>=1.32 0.08(stat.) GeV/c in d+Au
Charm Total Cross Section
1.13 0.09(stat.) 0.42(sys.) mb in 200GeV minbias Au+Au collsions
1.4 0.2(stat.) 0.4(sys.) mb in 200GeV minbias d+Au collisions
Charm total cross section per NN interaction
Charm total cross section follows roughly Nbin scaling from d+Au to Au+Au considering errors
Indication of charm production in initial collisions
Systematic error too large !
Experimental Statistical and Systematic Errors
c-cbar production CS PHENIX0.92+-0.15+-0.54 mb
STAR1.4+-0.2+-0.4 mb
Errors taken seriously
High pT region does not contribute to total CS much. STAR data need to be compared with PHENIX data!
Heavy Quarks Unique
Heavy Quark Flavors (Charm or Beauty)Heavy Flavors once produced –
do not change to light flavor easily heavy quark production can be calculated from pQCD approach more reliably than light quarks
Trace heavy quark flavors in nuclear collisions -- collision dynamics and hadronization mechanism
Fragmentation versus Recombination/CoalescenceFragmentation
p(heavy quark meson)/p(heavy quark) < 1
Recombination/Coalescencep(heavy quark meson)/p(heavy quark) >= 1
Nuclear Modification Factors
ddp
Nd
collddpNd
TAA
T
pp
T
AA NpR 2
2
/)(
Use number of binary nucleon-nucleon collisions to gauge the colliding parton flux:
N-binary Scaling RAA or RCP = 1 simple superposition of independent nucleon-nucleon collisions !
Peripheralcoll
T
Centralcoll
TTCP
NddpNd
NddpNd
pR
]/[
]/[
)( 2
2
Charm and Non-photonic Electron Spectra
1.13 0.09(stat.) 0.42(sys.) mb in 200GeV minbias Au+Au collsions
Total charm Binary Scalingsuppression at high pT
Charm Nuclear Modification Factor
STAR: Phys. Rev. Lett. 91 (2003) 172302
Suppressions!!
RAA suppression for single electron incentral Au+Au similar to charged hadrons at 1.5<pT<3.5 GeV/c
Heavy flavor production IS alsomodified by the hot and dense mediumin central Au+Au collisions at RHIC
electrons
K p d
electrons
hadrons
High pT Electron ID
dE/dx from TPC
SMD from EMC
hadrons electrons
High pT Electron ID
p/E from EMC
After all the cuts
The shape and yield at high pT
Note: FONLL – effective fragmentation functionharder than commonly used Peterson function!
STAR – difference ~ 5.5PHENIX -- ~1.7 (?)
Non-photonic electrons RAA
-- similar magnitude as light hadrons
-- STAR-PHENIX data consistent in the overlapping region
The high pT region n-p electron RAA
surprising !
Non-photonic electron RAA
Heavy quark energy loss: Early Expectations
k
E
M
dP
k
dkkdCdP Fs
,
)/1()(
0
2220
022
022
22
Y. Dokshitzer & D. Kharzeev PLB 519(2001)199
Radiative energy loss of heavy quarks and light quarks
--- Probe the medium property !
Heavy quark has less dE/dx due to suppression of small angle gluon radiation
“Dead Cone” effect
M. Djordjevic, et. al. PRL 94(2005)112301
J. Adams et. al, PRL 91(2003)072304
What went wrong?
Radiative Energy Loss not EnoughMoore & Teaney, PRC 71, 064904 (2005)
Large collisional (not radiative) interactions also produce large suppression and v2
Charm Quark in Dynamical Model (AMPT)
Large scattering cross sections needed !
Does Charm Quark Flow Too ?
Reduce Experimental Uncertainties !!Suppression in RAA Non-zero azimuthal anisotropy v2 !
B and D contributions to electrons
Experimental measurement of B and D contributions to non-photonic electrons !
Direct measurement of D and B mesons
Poor (Wo)Man’s Approach to Measure B/D Contributions to Electrons – e-h correlations
B
D
PYTHIA Simulations of e-h correlations from p+p
X. Lin hep-ph/0602067
B does not seem dominant at pT 4.5 GeV/c
Preliminary STAR Data
Xiaoyan Lin – STAR presentation at Hard Probe 2006
Open Issues
Phenix and STAR results Converge?!Systematic errors on non-photonic
electrons under control !Quantitative description for energy loss
and pT spectra for light/heavy quarksCollectivity for heavy quarks?
Recombination DS/D0
PYTHIA Prediction
Charm quark recombines with a light (u,d,s) quark from a strangeness equilibrated partonic matter DS/D0 ~ 0.4-0.5 at intermediate pT !!!
• J/ – Small: r ~ 0.2 fm
– Tightly bound: Eb ~ 640 MeV
HG
QGP Observed in
dileptons invariant mass spectrum
Other charmonia• ’ ~ 8%• ~ 32%
Color Screening
J/psi Suppression and Color Screening
cdiss
J
cdissdiss
TT
TTT
)25.1(
1.1
/
'
QCD Color Screening: (T. Matsui and H. Satz, Phys. Lett. B178, 416 (1986))
A color charge in a color medium is screened similar to Debye screening in QED the melting of J/.
c c Charm quarks c-c may not bindInto J/ in high T QCD medium
The J/ yield may be increased due to charm quark coalescence at the final stage of hadronization (e.g., R.L. Thews, hep-ph/0302050)
Recent LQCD Calculation:
dirdirdirJJ SSSS '// 1.03.06.0
J/ Quark Potential Model
Lattice QCD Calculations
J/ from di-lepton Measurements
J/-
PHENIX Data
Branching ratios: e+e- 5.93%; 5.88%
J/psi is suppressed in central Au+Au Collisions !
Factor ~ 3 the same as that at SPS
Satz: Only states are screened both at RHIC and SPS.
Alternative: Larger suppression in J/psi at RHIC due to higher gluon density, but recombination boosts the yield up !
V2 of J/psi
V2 of J/psi can differentiate scenarios !
pQCD direct J/psi should have no v2 !
Recombination J/psi can lead to non-zero v2 !
The case for partonic DOF/Deconfinement can be made with strange vector meson
cannot be made from KK coalescence !
J/ Suppression or NotNuclear Absorption of J/ important at low energy important (SPS) !
Both QCD color screening and charm quarkcoalescence are interesting, which oneis more important at RHIC?
At RHIC the J/ measurement requires highluminosity running!
Centrality and pT dependence important !
pT Scales and Physical ProcessesRCP
Three PT Regions:
-- Fragmentation
-- multi-parton dynamics (recombination or coalescence or …)
-- Hydrodynamics (constituent quarks ? parton dynamics from gluons to constituent quarks? )
Where does heavy quark fit?
The End